In a distribution system, a retailer or other product distributor (which may collectively be referred to as distributors) typically maintains an inventory of various items at one or more distribution centers, fulfillment centers, cross-docking facilities, materials handling facilities or warehouses (which may collectively be referred to as materials handling facilities). The inventory items are ordered from one or more vendors, received at the materials handling facilities as inbound shipments, and stocked in inventory of the materials handling facilities. In a conventional order fulfillment process, orders for items may be received from customers of the distributor. Units of the ordered items are picked from various locations in the inventory in the materials handling facilities, processed for shipping, and shipped as outbound shipments to the customers.
An example conventional order fulfillment process may include a pick process and a sortation process in which mixed batches of units picked for orders are sorted into their respective orders. In a conventional order fulfillment process, requests (e.g., orders) for items from requestors may be divided among multiple pickers, who then pick mixed batches of items. The orders may be subdivided among the pickers; therefore, two or more of the pickers may pick items for one order. Consequently, a sort operation to select the proper units of items for given orders from the aggregations of units items returned by each respective picker is required. Conventionally, sorting may be performed using automated sorting mechanisms or manual sorting systems. Automated sorting mechanisms for sorting certain types of inventory items according to individual orders include, but are not limited to, the Crisplant® sorter, Eurosort® sorters, and automated sorting mechanisms offered by other vendors. Using an automated sorting mechanism, batches or a stream of incoming picked items for multiple different customer orders are received at the automated sorting mechanism and sorted by the automated mechanism according to individual orders.
In typical automated sorting mechanisms, individual units of items are inducted from picked batches of mixed items directly onto the sortation mechanism into carriers (e.g., tilt trays) that are fixed to the sortation mechanism. Thus, typical automated sorting mechanisms that are used in materials handling facilities tend to be linear sorting systems. Linear sorting inducts or places individual units of items from picked batches of items (referred to as singulation) onto an individual tray or transport mechanism that is a fixed component of a linear piece of automated equipment. All of the trays or transport mechanisms are connected in a linear sequence (typically in a circle or oval continuously-running loop). An item is placed directly onto a carrier of the automated sorting mechanism. Linear sorting systems thus tend to be limited in velocity, total capacity, and the size and types of items that can be sorted.
Robotics in Order Fulfillment Systems
Order fulfillment systems exist in which mobile robotic devices are employed. In a conventional order fulfillment system that employs robotic devices, an order fulfillment center includes one or more workstations. An operator at each workstation is assigned a set of one or more orders to fulfill from inventory; typically, four to twenty orders are assigned to a workstation in a set. To fulfill the current set of orders at a given workstation, the mobile robotic devices pick up and deliver portable inventory storage units from a stock storage area to the work station, where the operator picks items from the storage unit and places the items into shipping boxes or slots assigned to particular orders in the current set. The mobile robotic devices deliver shelving units to the workstation until all of the orders in the current set of orders assigned to the work station are fulfilled from inventory. At that time, the fulfilled orders are moved from the workstation to downstream stations where the shipping boxes are sealed and shipped, and a new set of boxes or slots for a new set of orders is moved to the workstation to start the process over again.
The conventional order fulfillment system employing robotic devices described above is serialized; all inventory for a particular order has to come to a particular workstation that is assigned that order. In such conventional systems, the number of workstations required and therefore the capacity of the system is tied to how quickly (cycle time) all items for an order can be delivered to the workstation from the time an order is assigned to a particular workstation and the time the last item for the order is pulled from a storage units at the workstation. Thus, the delivery of inventory to a workstation quickly and without delay is critical to the success of the conventional system. Orders at a workstation may have to wait for fulfillment while needed inventory storage units are being delivered to and processed at one or more other workstations. This is particularly the case where a given storage unit may store many different types of items, as the likelihood that two or more workstations may need the same storage unit at the same time goes up as the number of types on the storage unit increases. Particular orders can be delayed waiting for inventory if the size of the inventory storage area is very large as inventory must travel to a specific workstation to be fulfilled regardless of distance traveled. To maintain efficiency, this conventional robotic order fulfillment system may require frequent tuning, for example by rearranging the distribution of items or storage units in inventory storage, in attempts to minimize the movements of the robotic devices and thus maximize throughput of the system. This optimization may be effective when few types of units are stored in inventory (e.g., thousands) and there are large quantities of each unit type (e.g., hundreds/thousands) but ineffective when many types of units (e.g., hundreds of thousands/millions) and few units (e.g., tens/hundreds) of each are stored. This large number of unit types with few units of inventory each increases the odds a storage unit could be required at any given workstation to fulfill an order. This lack of optimization creates longer cycle times which require more workstations which create more competing demands for inventory storage units which reduce cycle times and therefore creates a downward spiral of system throughput once this condition occurs. While this conventional robotic order fulfillment system may work well for single-floor, relatively small distribution centers (up to 100k-200k square feet) with relatively few types of items, the system is difficult to scale to larger distribution centers (200k+ square feet), distribution centers with tens of thousands to millions of types of items, and multi-level distribution centers. In addition, this conventional robot-assisted order fulfillment system is an end-to-end order fulfillment solution, and is difficult to integrate with other materials handling techniques resulting in reduced flexibility and increased costs when supporting non-level system demand.
While embodiments are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that embodiments are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to.